Suspended and solute loads on the Lower Diyala River
N.A. AL-ANSARI, G.T. AL-SINAWI & A.K. JAMIL University of Baghdad College of Science Department of Geology
ABSTRACT The Diyala weir which is about 11 Km downstream from Hemrin reservoir, distributes the outflow of Hemrin reservoir to the Lower- Diyala River and the irrigation cannais (Khalis and Sadr Al-Mushtarak). Suspended sediment and solute loads associated with the Lower Diyala River were evaluated for the period June/ 1984 - May/1985. During the studied period the mean discharge reached 128 cumecs and the maximum and minimum were 505 and 1.72 cumecs respectively. The annual suspended load reached 64589 tonnes (rate of erosion 2.17 ton/km2) forming five percent of the total load. The annual solute load reached 1.24 x 10^ tonnes (rate of erosion 42.00 ton/km^) which forms 95 percent of the total load. The rate of transport was not uniform throughout the studied period, where most of the load (51.02 percent of the suspended load and 54.68 percent of the solute load) was transported during the Winter.
INTRODUCTION
The River Diyala, a tributary of River Tigris, is one of the important rivers in Iraq draining an area reaching 32600 km^. Two dams were constructed on the river, Derbendikhan and Hemrin (360 and 188 km upstream the confluence with the Tigris river south Baghdad respectively)(Figure 1). In addition to the two dams, the Diyala wier was constructed on the river (11 km downstream from Hemrin Dam) and it distributes the outflow of Hemrin reservoir to the Lower Diyala River and the irrigation cannais (Al-Khalis canal and Sadr Al-Mushtarak). A total of 314 samples were collected at the Hemrin station at daily intervals.
FLOW CHARACTERISTICS
Derbendikhan and Hemrin stations are the oldest stations on Diyala River with records dating back to 1957 and 1932 respectively (Ministry of Irrigation, 1976; & 1983).
Derbendikhan Station
It drains an area of 17800 km 2 and the hydrological records indicate that the mean daily discharges for the period 1957 - 1984 reaches 170 cumecs while the maximum and minimum daily discharges were 2280 and 1 cumecs respectively. Through the same period 10 years were wet with an average annual discharge of 244 cumecs and 18 dry years with an average annual discharge of 129 cumecs. The slope of the river between Derbendikhan and Diyala weir is relatively steep (1.6 m/km) .
Hemrin Station
It drains an area of 29700 km^ and the hydrological records indicate that the mean daily discharges for the period 1932 - 1984 reaches 179 cumecs 225 basin.
River
Diyala
1:
Figure
226 Table 1 Suspended and solute concentration at Hemrin site (Lower Diyala River) for the period June/1984 - May/1985.
Year Month Sus. Sed. Solute Cone. Water Discharge Cone, ppm ppm m^/sec
June 18.08 456.270 9.50 July 3.45 424.900 8.47 Aug. 4.65 325.806 6.12 S Sep. 4.09 302.200 4.246 Oct. 5.84 273.900 4.553 Nov. 51.28 532.640 56.211 Dec. 16.01 296.96 231.584
Jan. 13.79 324.800 216.318 Feb. 14.73 317.330 441.250 2 March 8.73 327.083 279.645 T—1 April 23.45 306.300 231.324 May 11.61 357.200 51.190 while the maximum and minimum daily discharges were 3340 and 12 cumecs respectively. Through the same period 19 years were wet with an average annual discharge reaching 262 cumecs and 35 dry years with an average annual discharge reaching 135 cumecs. The slope of the river for the strech between Diyala weir and its confluence with Tigris River south of Baghdad is relatively gentle (0.11 m/km). The tributaries which flow into the river within the stretch between Derbendikhan and Hemrin caused an increase of the water discharge at Hemrin station between 1-34 percent. It should be mentioned however, that 11 years of the record are exceptional in that the discharge at Derbendikhan was higher than Hemrin. This period represents either dry years or impounding by Hemrin dam.
SUSPENDED MATTER
The concentrations and loads of the suspended matter in the river was established during the studied period.
Suspended Sediment Concentration
The mean daily concentration at Hemrin station reached 13.8 ppm and the maximum and minimum concentrations were 230 ppm (14/11/1984) and 0.4 ppm (10/6/1984). The mean monthly concentrations ranged between 3.48 ppm during July/1984 and 51.28 ppm during Nov./1984 (Table 1). The sudden increase in water discharge (about 12 fold) at Nov./1984 caused an increase of the suspended sediment concentration to about 9 fold which is a normal case in natural rivers (Allen, 1974 and Bagnold, 1980). No significant relationship between water discharge and suspended sediment concentration was recognized (Figure 2) due to the effect of Hemrin reservoir which is the logical case in rivers effected by reservoirs (Smith and Alexander, 1984). It should be noted that a clear
227 IOD
IC 100 100: Vater discharge n^/sec
Figure 2: The relationship between suspended sediment concentration and water discharges at Hemrin station. relationship was recognized by Assad (1978) for the same site before the construction of Hemrin dam.
Suspended Sediment Load
The total suspended sediment load associated with the lower Diyala River reached 64589 tonnes (rate of erosion 2.17 ton/km^) with a daily average of 177 ton/day which forms 65.5 percent of the suspended sediment load leaving Hemrin reservoir. The maximum and minimum loads were 4568 ton/day (30/4/1985) and 0.12 ton/day (2-22/9/1984) respectively. The monthly load ranged between 46.6 tonnes during Sep./1984 and 15561 tonnes during Feb./1985 (Table 2). These values were very low relative to those found by Assad (1978) and Al-Ansari et al. (1983c) before the construction of Hemrin Dam and are lower than those found for other catchments in Iraq (See Al-ansari et al., 1983a,b; Al-Ansari and Toma,
228 Figure 3: Relationship between water discharge and suspended load at lower Diyala River.
1985; Al-Jabbari and Mansour, 1986; Al-Ansari and Ali, 1986; and Al- Ansari et al., 1986). These differences are due to the effect of Hemrin reservoir and different geological, geomorphological and hydrological conditions. The data also indicate that 0.7 percent were transported during summer, 12.4 percent during autumn, 51 percent during winter and 35 percent were transported during spring. A direct linear relationship was established for the relationship between water discharge and suspended sediment load (Figure 3) as represented in equation (1).
Log y = Aj log x + Ao ...... (1) where x = water discharge y = sediment discharge Ao = -0.575 and A = 1.218
SOLUTE MATTER
Concentrations and loads of solute matter for Diyala River were established during the studied period.
Solute Concentration
The mean daily concentration at Hemrin station reached 354.12 ppm and the maximum and minimum concentrations were 902 ppm (28/11/1984) and 36 ppm
229 loooo
Water Dibcharge ( nA btc.) Figure 4: Relationship between water discharge and dissolved material at Hemrin station.
(30/9/1984) respectively. The mean monthly concentration ranged between 273.9 ppm during Oct./1984 and 532.64 ppm during Nov./1984 (Table 1). The solute concentration was almost uniform for all water discharges (Figure 4) but showed a slight indication of direct relationship at low discharges (less than 40 cumecs). This reflects the effect of Hemrin reservoir and the low velocity of the out flow on the solute concentration. At higher discharges however the points are more scattered and show an inverse relationship due to the effect of rainfall and snowmelt.
Solute Load
The total solute load associated with lower Diyala River reached 1246002 tonnes (rate of erosion 41.949 ton/km^) with an average daily rate of 3414 ton/day. The maximum and minimum loads were 25122 ton/day (6/2/1985) and 11 ton/day (30/9/1984) respectively. The total monthly load ranged between 3345 ton/month during Sep./1984 and 324671 ton/month during Feb./1985 (Table 2), which differs from the solute load in other
230 Table 2 Suspended sediments and solute loads associated with the Lower Diyala River for the period June/1984 - May/1985.
Year Month Sus. Load Solute Load Ts/Td Ton/month Ton/ Ton/month Ton/ Km^/month Km2/month (Ts) (Td)
June 321 0.011 10189 0.343 0.032 July 72.3 0.0024 9151 0.308 0.0077 Aug. 73.6 0.0025 5350 0.180 0.013 00 Sep. 46.6 0.0015 3345 0.112 0.013 Oct. 70.4 0.0023 3725 0.125 0.018 Nov. 7907.0 0.2660 87152 2.934 0.090 Dec. 8549.0 0.287 172393 5.804 0.049
Jan. 8866.0 0.298 184111 6.199 0.048 Feb. 15561.0 0.523 324671 10.931 0.047 2 March 7890.0 0.265 228549 7.695 0.034 2 April 13291.0 0.447 171508 5.774 0.077 May 1942 0.065 45858 1.544 0.042
basins in Iraq (Al-Ansari and Ali, 1986; and Al-Jabbari and Mansour, 1986) due to different geological and morphological conditions and the presence of Hemrin reservoir. The data also indicate that 1.98 percent of the load was transported during summer, 7.56 percent during autumn, 54.68 percent during winter and 35.78 percent was transported during spring. The solute rating curve (Figure 5) showed a direct but not linear relationship where the increase rate of water discharge was greater than that of solute discharge for high water discharge conditions. In addition the relationship was more correlated at low discharges which suggests that dilution processes occur during wet months. The relationship between water discharge and solute discharge was presented in equation (2).
Log y = A2 log x2 + Aj log x + Ao ...... (2)
where x = water discharge y = solute discharge Ao = 1.3305 A| = 1.269 and A2 = -0.0986
THE RELATIVE MAGNITUDE OF DISSOLVED AND SUSPENDED LOADS
The total load associated with the Lower Diyala River during the studied period was 1310600 tonnes where 95 percent was solute load. The ratio between suspended load (Ts) and solute load (Td) ranged between 0.0077 (July/1984) and 0.090 (Nov./1984) (see Table 2).
231 POLYNOMIAL MODEL: Y«RCN>*XAM+f
I
1 10 100 1000 Water discharge a^/aec
Figure 5: Relationship between water discharge and total dissolved solids discharge at lower Diyala River.
A linear direct relationship between suspended and solute loads is shown in Figure 6 and presented in equation (3).
log y = Aj log x + Ao (3) where x = suspended load y = solute load Ao = 1.113 and Ax = 0.721
This type of relationship agrees with that found by Meybeck (1976). The data indicate a direct relationship between water discharge and the ratio Ts/Td also as it is shown in Figure 7. Such relations indicate that both loads have similar response to the influence of external processes.
CONCLUSIONS
Suspended sediment and solute loads were investigated at Hemrin station for the period June, 1984 - May, 1985. Throughout this period 314 samples were collected and analyzed. The mean daily suspended sediment concentration at Hemrin station reached 13.8 ppm ranging from 0.4 ppm (10/6/1984) to 230 ppm
232 to w W
IS ton/}an2/moiith
Figure 6: Relationship between suspended and solute load. Figure 7 : Relationship between average monthly discharge and the ratio between suspended and dissolved loads (Ts/Td).
(14/11/1984). The suspended sediment load associated with lower Diyala River reached 64589 tonnes (rate of erosion 2.17 ton/km^) with an average daily rate of 177 tonnes. The maximum and minimum daily loads were 4568 ton/day (30/4/1985) and 0.12 ton/day (2-22/9/1984) respectively. Most of the suspended load (51 percent) was transported during winter. The mean daily solute concentration at Hemrin station reached 354.12 ppm ranging from 36 ppm (30/9/1984) to 902 ppm (28/11/1984). The solute load associated with Lower Diyala River reached 1.246 x 10^ tonnes (rate of erosion 42.00 ton/km^) with an average daily rate of 3414 tonnes. The maximum and minimum daily loads were 25122 ton/day (6/2/1985) and 11 ton/day (30/9/1984) respectively. About 54 percent of the solute load was transported during winter.
REFERENCES
Al-Ansari, N.A., Ali, S.H. & McManus, J. (1983a) Sediment discharge in River Adhaim (Iraq). Journ. Water Resources 2(2), 1-22. Al-Ansari, N.A., Al-Jabbari, M.H. & Al-Sinawi, G.T. (1983b) Calculation of sediment discharge for the period 1975-1981 in the River Adhaim
234 (Iraq). Second International Conference on River Sedimentation China, 1105-1111. Al-Ansari, N.A., Al-Jabbari, M.H. & Madhat, A. (1983c) Sediment discharge in Hemrin Dam Reservoir. Second International Conference on River Sedimentation China, 1098-1104. Al-Ansari, N.A. & Toma, A. (1985) Suspended sediment waves in the River Tigris, Sari station for the year 1982. Intern. Symp. Erosion, Debris Flow and Disaster Preventation (ISEDD), 157-162. Al-Ansari, N.A., Al-Jabbari, M.H. & Al-Sinawi, G. (1986) Suspended sediment in the upper parts of River Euphrates. Journ. Water Resources 5(1), 67-83. Al-Ansari, N.A. & Ali, J. (1986) Suspended load and solute discharge in River Tigris within Baghdad. Journ. Water Resources 5(1), 35-50. Al-Jabbari, M.H. & Mansour, N. (1986) Sediment discharge in Adhaim River within drought conditions. Journ. Water Resources 5(1), 117-134. Allen, J.R.L. (1974) Reaction, Relaxation and Lag in natural sedimentary systems; general principles, examples and lessons. Earth Science Reviews 10, 263-342. Assad, N.M. (1978) Sediments and sediment discharge in the River Diyala. M.Sc. Thesis Univ, of Baghdad (Unpubl.) 157p. (in Arabic). Bagnold, R.A. (1980) An empirical correlation of bed load transport rates in flumes and natural rivers. Proc. Roy. Soc. (London) 372, 453- 473. Meybeck, M. (1976) Total mineral dissolved transport by world major rivers. Hydrological Science Bull. 21, 265-284. Ministry of Irrigation (1976) Discharges for selected gauging stations in Iraq (1959-1975). Director General of Irrigation, Rep. of Iraq. 374p. Ministry of Irrigation (1983) Discharges for selected gauging stations in Iraq (1976-1982). State Organization for maintenance and operation of irrigation projects, Rep. of Iraq. 166p. Smith, R.A. & Alexander, R.R. (1984) Trends in concentrations of dissolved solids, suspended sediments, phosphorous and inorganic Nitrogen at U.S. Geol. Survey National Stream quality accounting network stations. U.S. Geol. Survey water supply paper 2275 66-73.
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